Continuous pickling line for endless sheets

ABSTRACT

A pickling line for continuously travelling endless sheets consisting of a subdivided acid trough 1 with individual cover plates 20 removable in sections, a driving device 31 for pulling the sheet and a loop pit 24 mounted in front of the acid trough without means to effect a back pull.

United States Patent Inventors Appl. No.

Filed Patented Assignee Priority Rudolf Speelmanns Hilden (RhldJ;

Freidrlch Wilhelm Delwig, Dusseldorf, both of Germany May 16, 1969 Dec. 7, I971 Moeller & Neumann Gmbll lngbert Saar, Ensheimer Str., Germany May 16, 1969 Germany CONTINUOUS PICKLING LINE FOR ENDLESS SHEETS 5 Claims, 2 Drawing Figs.

05. Cl 134/122, 134/ l 5 Int. Cl B08b 3/08,

[50] Field ofSearch 242/7552;

134/9, l5,64,75, I22, I54, l83, l82

[56] References Cited UNITED STATES PATENTS 2,l47,467 2/1939 Stephenson 242/7552 X 2,2l6,544 [0/1940 True et al. 134/64 2,709,l43 6/l955 Francis et al. 134/64 X 2,898,627 8/1959 Bley et al. 134/64 X Primary Examiner-Thomas F. Callaghan Assistant Examiner-David H. Corbin Arlurney-John J. Dennemeyer ABSTRACT: A pickling line for continuously travelling endless sheets consisting of a subdivided acid trough l with individual coverplates 20 removable in sections, a driving device 31 for pulling the sheet and a loop pit 24 mounted in front of the acid trough without means to effect a back pull.

CONTINUOUS PICKLING LINE FOR ENDLESS SHEETS The invention relates to a pickling line for receiving a continuously travelling endless sheet comprising an acid trough subdivided by cascade walls and a loop pit mounted on the inlet side, and at the outlet side a device for pulling the sheets through the acid bath in the trough. in the usual pickling lines an adjustable counter pull is exerted on the sheet by a pair of driving rollers mounted on the inlet side. The relationship between the speed of the driving device on the inlet side and on the outlet side to maintain a relative uniformity of the loop or more specifically the amount of loop sag is controlled by a loop-tracing device disposed in the floor of the acid trough. The permissible sheet tension resulting from the height of the loop sag requires in this case a high acid level of about 1,200 mm. False signals of the loop-tracing device due to a position change of the sheet and inaccuracies resulting from the varying sheet dimensions cause occasionally excessive sheet tensions which produce a tearing or ripping of the sheet.

A sheet rip inside a continuously operating pickling line causes considerable production losses especially in the case of a hydrochloric acid bath. In contrast to sulfuric acid the hydrochloric acid develops a much more poisonous and aggressive gas. However, it will be understood that the invention is not limited to the use of a hydrochloric acid bath. In the case of a band rip it is necessary to suppress the development of gas by lifting several cover plates, and after locating the ripped part of the sheet by applying a foam layer on the bath surface. Simultaneously the temperature of the pickling fluid must be lowered in order to diminish the gas development. It is also frequently necessary to cover up motors and other machines and tools located in the vicinity. The rust which is formed on the metal parts of the entire work area must be removed at high maintenance costs.

After the cover plates have been removed it is a tedious job to find and pull up the sheet ends lying in the acid bath, and welding them together again with suitable tools.

All these difficulties are caused due to the excessive sheet tension from which depends in turn the high acid level which makes it economically prohibitive to simply draw off the acid when a sheet rip has occurred.

It is an object of this invention to eliminate the above mentioned difficulties particularly in pickling lines using hydrochloric acid as pickling fluid. It is based on the recognition that a reduction of the bath height or of the acid level should be made feasible so that it would be practical to draw off the acid from individual chambers at least in the area of the sheet rip. This is obtained according to the invention in that the loop pit is mounted directly in front of the acid trough trough so that it is not subjected to any drag or back tension. Accordingly no driving roller pair or similar device exerting a continuous back tension on the sheet is provided between the loop pit and the inlet opening of the sheet. The result of this measure is that the bath level or the acid volume may be chosen freely, e.g. 500 mm. instead of [.200 mm. With a thus low acid volume it is economically feasible to draw off the pickling fluid during idle periods or after a sheet rip in order to eliminate the disturbance or break while the acid container is empty and without danger to the personnel. As a side effect of the tension-free drawing of the sheet through the pickling line the danger of sheet rips is substantially diminished and perhaps even completely eliminated.

A low acid level of 300-400 mm. is already known in a discontinuously operating pickling line using a sulfuric acid bath.

Since in a discontinuous pickling operation the sheets are not welded together to form an endless strip and consequently there is also no danger of a rip in the strip nor the resulting delays in operation the concept of drawing the strip of sheets through a continuous pickling line without back tension, especially with a hydrochloric acid bath, was not an obvious conclusion.

ln order to maintain the endless sheet positively inside the pickling fluid in spite of the low acid level immersion rollers are provided in a known manner on the inlet and outlet side of the pickling trough in order to hold the endless sheet down.

In order to empty the individual chambers in a selective manner each chamber is provided according to another feature of the invention with i an outflow which leads into a separate collector vessel from which the acid may be pumped back into the trough or chambers.

When a sheet rip has been localized and one or more of the cover plates have been removed it is necessary only to remove the gas from the chamber adjacent the sheet rip since an emptied chamber may be separated or subdivided according to a further feature of the invention from the adjacent chamber or within itself by separation walls which may be inserted and removed as required. For this purpose the separation walls are provided with a bridging-strip for covering a joint or gap provided between two adjacent cover plates and covered during operation, and the separation walls are supported through the bridging-strips against the cover plates. Accordingly one merely has to remove a joint strip and to position immediately a separation wall in order to close the joint again. lf on both sides of an acid chamber to be emptied such separation walls are positioned the intermediate cover plates may be removed if previously the acid has been drained off and the gas accumulated between the separation walls has been evacuated.

The separation walls are suitably provided at the edge with a resilient sealing strip extending on three sides so that they may positively fulfill their task of providing a gastight separation between emptied trough chambers.

The above objects and features of the invention will become apparent from the following description when taken in connection with the annexed drawing showing a continuously operating pickling line according to the invention and in which FIG. 1 illustrates the first two chambers of the pickling trough with the loop pit positioned in front of the trough, and

FIG. 2 shows the two last pickling chambers completing the trough.

The main part of the pickling line is the acid trough l which is subdivided by three cascade walls 2 into four chambers 3, 4, 5 and 6. Each chamber is provided with a drainage line 7, 8, 9 and 10 having a stop valve 12, 13, 14 and 15 respectively so that the acid of each chamber may be discharged into collector vessels 16, 17 18 and 19. By means of one or more pumps the acid may be returned into an emptied chamber. The arrangement of individual collector vessels has the advantage that with respect of an economical regeneration of the pickling fluid the desired graduation of the Fe content by the subdivision of the acid trough into separate chambers is not lost by the mixing of acid from adjacent chambers.

The chambers 3, 4, 5 and 6 are covered by a number of cover plates 20. The cover plates 20 have between them joints which are covered up during operation by bridging strips 21 and their significance will be explained in greater detail hereafter.

The loop pit 24 is positioned directly in front of the acid trough 1 so that the endless sheet 25 travels out of the loop into the pickling line without being retained by a driving roller pair or similar device. A roller set 26 is mounted in front of the trough inlet merely for the purpose of providing a centering o the endless sheet to assure the input of the endless sheet in a centered position over a support roller 27 into the trough. The loop produced between a driving roller pair 28 or similar device mounted in front of the loop pit 24 and the roller set 26 is maintained at a suitable level by means of light gates 30 and the driving roller pair 28.

The endless sheet 25 is pulled through the acid trough l by the pulling force of a driving roller pair 31 or similar device mounted at the outlet side of the trough while immersion rollers 32, 33 mounted respectively at the inlet and outlet end of the trough retain the sheet inside the pickling fluid. Accordingly the sheet is not subjected to any back pull generated by a special device mounted at the inlet side. For this reason the acid level can be maintained low such as for example at 500 mm. as shown in the present embodiment.

During short idle periods (less than 2 hours) the sheet is lifted in a known manner by means of a sheet lifter out of the pickling fluid. A suitable number of sheet clamps (not shown) provided at the inlet and outlet side are used during this operation to maintain the sheet in a stretched position When the pickling line is not operated for a more extended period during which the aggressive gas of an hydrochloric acid bath would attack and cause excessive pickling of the raised sheet itself the entire pickling fluid which is less voluminous due to the lower bath level is drained in this case into the collection vessels 16 through 19. Upon resumption of the operation it is pumped back into the pickling chamber in a very short time.

In the case where the work stoppage has been caused by a sheet break only that chamber is emptied in which the two broken sheet ends are located. Assuming that the break has occurred in the second half of chamber 3 only this chamber 3 is emptied by actuating valve 12. Thereafter the cover strips 21 which close the joints between the cover plates are removed on both sides of the sheet break at a sufficient distance and in these places dividing walls 34, 35 are inserted which separate that part of chamber 3 containing the sheet break from the adjacent chambers. Since the cover plates 20 disposed between the dividing walls must be removed in order to get access to the place where the sheet break has occurred the dividing walls 34. 35 with their cover strips 34a, 35a are supported merely on one side on a remaining cover plate 20. If the dividing walls 34, 35 are inserted at a greater distance from each other they may be supported on two remaining adjacent cover plates 20. Between the time where the acid is drained off or the insertion of the dividing walls and the removal of the cover plates 20 there is a short wait so that the greatest portion of the gas volume may be drawn off by a conventional suction installation not shown. Thereafter the cover plates 20 are removed. When the open chamber area is then cleaned with water a further formation ofgas is eliminated.

After the dividing walls according to the invention have been inserted it is not possible simply to pull the sheet ends together as it has been done hitherto and to weld them back together again. Accordingly it is within the scope of the invention to provide the sheet ends with holes with allow the application ofa flexible device entering the holes in each sheet end and covering the gap in the sheet.

After the sheet gap has been closed in this manner the cover plates 20 are replaced, the dividing walls 34, 35 are removed, the joints are closed again by means of the bridging strips 21 and the bath fluid is pumped back from the collection vessel 16 into the chamber 3. Immediately thereafter the operation may be continued especially when the bath fluid in the collecting vessel 16 has been maintained at the proper temperature.

In contrast to the measures required hitherto when sheet breakage has occurred the invention offers considerable advantages in time savings and additionally in connection with use of hydrochloric acid as pickling fluid a greater safety in handling aggressive acids.

We claim:

1. A continuous pickling line for endless sheets comprising, in combination, an elongated trough having an interior for containing a bath of pickling fluid, said trough having an inlet end and an outlet end for admitting and discharging respectively an endless sheet advancing continuously through said bath in said trough interior, a plurality of longitudinally spaced, cascade walls in said trough interior, said cascade walls being arranged to divide said trough into a plurality of chambers. sheet pulling means associated with said trough adjacent said trough outlet end for advancing said sheet continuously in said trough through said bath in said chambers with said sheet in overlying, sliding engagement with said cascade walls and a loop pit associated with said trough adjacent said inlet end for maintaining a loop in said sheet prior to the admission ofsaid sheet into said trough inlet end.

2. A continuous pickling line in accordance with claim 1 including drain means on said trough operatively associated with each of said chambers for draining the pickling fluid selectively from said cha mbe rs. I

3. A continuous pickling line In accordance with claim 1 including guide rollers operatively associated with said trough adjacent said trough inlet end for guidably supporting said sheet advancing from said loop pit into said trough inlet end. an immersion roll in said trough adjacent said inlet end for guidably directing said advancing sheet into said bath and an immersion roll in said trough adjacent said outlet end for guidably directing said advancing sheet out ofsaid bath.

4. A continuous pickling line in accordance with claim I including a plurality of longitudinally spaced, cover plates for closing the top of said trough, each pair of adjacent cover plates having edge portions defining therebetween a transversely extending upper opening in said trough, removable means for closing each of said trough upper openings at least two separation walls arranged to be positioned in said trough within at least two of said upper openings in sealing relationship with the inner wall ofsaid trough and in vertically extending, longitudinally spaced relationship to define therebetween a subchamber from which said pickling fluid is to be drained.

5. A continuously pickling line in accordance with claim 4 including a bridging strip on the upper edge of each of said separation walls, said bridging strip arranged to be positioned in overlying, sealing engagement with said edge portions of said adjacent pair of cover plates in said trough upper opening with said separation wall positioned in said trough. 

1. A continuous pickling line for endless sheets comprising, in combination, an elongated trough having an interior for containing a bath of pickling fluid, said trough having an inlet end and an outlet end for admitting and discharging respectively an endless sheet advancing continuously through said bath in said trough interior, a plurality of longitudinally spaced, cascade walls in said trough interior, said cascade walls being arranged to divide said trough into a plurality of chambers, sheet pulling means associated with said trough adjacent said trough outlet end for advancing said sheet continuously in said trough through said bath in said chambers with said sheet in overlying, sliding engagement with said cascade walls and a loop pit associated with said trough adjacent said inlet end for maintaining a loop in said sheet prior to the admission of said sheet into said trough inlet end.
 2. A continuous pickling line in accordance with claim 1 including drain means on said trough operatively associated with each of said chambers for draining the pickling fluid selectively from said chambers.
 3. A continuous pickling line in accordance with claim 1 including guide rollers operatively associated with said trough adjacent said trough inlet end for guidably supporting said sheet advancing from said loop pit into said trough inlet end, an immersion roll in said trough adjacent said inlet end for guidably directing said advancing sheet into said bath and an immersion roll in said trough adjacent said outlet end for guidably directing said advancing sheet out of said bath.
 4. A continuous pickling line in accordance with claim 1 including a plurality of longitudinally spaced, cover plates for closing the top of said trough, each pair of adjacent cover plates having edge portions defining therebetween a transversely extending upper opening in said trough, removable means for closing each of said trough upper openings at least two separation walls arranged to be positioned in said trough within at least two of said upper openings in sealing relationship with the inner wall of said trough and in vertically extending, longitudinally spaced relationship to define therebetween a subchamber from which said pickling fluid is to be drained.
 5. A continuously pickling line in accordance with claim 4 including a bridging strip on the upper edge of each of said separation walls, said bridging strip arranged to be positioned in overlying, sealing engagement with said edge portions of said adjacent pair of cover plates in said trough upper opening with said separation wall positioned in said trough. 